1. Field of the Invention
The present invention relates to a piezoelectric actuator device comprising a piezoelectric actuator element.
2. Description of the Related Art
Piezoelectric actuator elements are generally used for volume control, switches, or ink jet droplet control since they expand or contract when a voltage is applied to generate a displacement that is practically proportional to the applied voltage.
However, when a voltage is directly applied to such piezoelectric actuator element, the amount of displacement of the piezoelectric actuator element due to a process that is increasing the applied voltage differs significantly from the amount of displacement due to a process that is decreasing the applied voltage. In other words, a large hysteresis occurs in the amount of displacement of the piezoelectric actuator element. As a result, the amount of displacement of the piezoelectric actuator element for an applied voltage cannot be confirmed.
As a means of solving the abovementioned problem, Japanese Patent Publication No. 1997-327181A or Japanese Patent No. 2836328, for example, discloses a technique for detecting the amount of displacement of a piezoelectric actuator element and performing feedback control on the piezoelectric actuator element according to this detection signal. However, with this conventional technique, a feedback control circuit is required, making the system configuration more complex.
As another means of solving the abovementioned problem, Japanese Patent Publication No. 1988-20472A or Japanese Patent Publication No. 1989-202178A discloses a configuration in which a capacitor is connected in series with a piezoelectric actuator element. However, with this conventional technique, a voltage that is extremely higher, for example, several times to several tens of times higher than the normal applied voltage for a piezoelectric actuator element must be applied to the series circuit comprising the piezoelectric actuator element and capacitor. A special configuration is required to apply such a high voltage, which prevents the device from being made more compact.